Tungsten heavy alloy materials are known in the art for use in various applications, including, among others, ballistic devices. In the past, tungsten heavy alloys have been fabricated by liquid phase sintering of mixed elemental powders. The material resulting from such liquid phase sintering generally comprises a two phase composite consisting of rounded tungsten grains dispersed in an alloy matrix. While resulting materials have exhibited sintered densities in excess of 99.5 percent of the theoretical density values, and high ductility and strength, it has been difficult to control the property uniformity and to consistently provide the maximum attainable properties.
Generally, the mechanical properties of the alloy materials are strongly dependent on the specific microstructural characteristics of the materials. The most prominent of these characteristics are the contiguity, the dihedral angle and the volume fraction of the tungsten phase. Ideally, for a given tungsten content, the optimal microstructure should exhibit low contiguity, a low dihedral angle, small grain size and strong tungsten-tungsten grain boundaries and tungsten-matrix interface. However, in practice, it appears that there is a clear tradeoff of these properties. For example, it appears that a low dihedral angle can be induced by higher tungsten solubility in the matrix phase which is possible through alloying or the use of higher sintering temperatures. Conversely, there is grain growth penalty owing to the use of higher sintering temperatures. Accordingly, it would be advantageous to provide a means for independently controlling the grain size, the dihedral angle and the contiguity.
Tungsten heavy alloy materials have also been produced using solid state sintering methods whereby finer microstructures, for example, of from two to three .mu.m tungsten particle size, are obtained as compared with the liquid phase sintered products, having tungsten particle sizes of from 30 to 50 .mu.m. However, solid state sintering provides materials having high contiguity and therefore the materials are extremely brittle. The use of very fine powders, for example, 0.1 .mu.m in diameter, results in materials having a microstructure exhibiting low ductility.
Thus, a need exists for improved tungsten heavy alloy materials which have both fine grain size and low contiguity, and therefore exhibit both high strength and good ductility, and methods for the production of such materials.